Author:

Caitlin Thompson

Mentor:

Lee Kats, Professor of Biology , Pepperdine University

Caddisflies are small insects which spend their larval stages enclosed in cases on the streambed of freshwater streams and feed on organic material and leaf litter. Several species exist, some of which build cases out of organic material such as leaves and twigs (leafy), while others use sediment, sand and rock fragments (sandy). Caddisflies inhabiting streams in the Santa Monica Mountain Range face predation from numerous organisms, one of which is the invasive crayfish, Procambarus clarkii. In previous studies it has been shown that (1) caddisflies inhabiting leafy cases are more prone to predation from crayfish than are their leafy counterparts and (2) leafy caddisflies are able to build cases out of sediment and sandy flies are likewise able to use organic material for construction. A tradeoff seems to exist between sandy and leafy cases since, although less reliably protected, leafy caddisflies continue to build fragile leafy cases. The purpose of this experiment was to examine possible benefits of a leafy case and it was hypothesized that a caddisfly could consume part of their casing for nutrition when faced with a shortage of food. Leafy caddisflies were removed from their case and the case was weighed. Half of the cases were used as a control group while the other half were placed in containers with one living caddisfly. The cases were left in a temperature controlled unit for 7 days and were reweighed at the end of this time; the cases with the caddisflies were found to have lost a significantly greater mass, a result which seems to indicate that there is indeed a benefit for building leafy cases.